The present invention relates generally to the field of electronic data storage and retrieval, and more particularly to a perpendicular magnetic writer with a magnetically soft and stable high magnetic moment main pole.
Perpendicular recording potentially can support much higher linear density than longitudinal recording due to lower demagnetizing fields in recorded bits, which diminish with linear density increase. To provide decent writeability, double layer media are used. The double layer perpendicular media consist of a high coercivity, thin storage layer with perpendicular to-plane anisotropy and a soft magnetic keeper (underlayer) having in-plane anisotropy and relatively high permeability.
A magnetic head for perpendicular recording generally consists of two portions, a writer portion for storing magnetically-encoded information on a magnetic media (disc) and a reader portion for retrieving that magnetically-encoded information from the media. The reader portion typically consists of a bottom shield, a top shield, and a sensor, often composed of a magnetoresistive (MR) material, positioned between the bottom and top shields. Magnetic flux from the surface of the disc (media) causes rotation of the magnetization vector of a sensing layer of the MR sensor, which in turn causes a change in electrical resistivity of the MR sensor. The change in resistivity of the MR sensor can be detected by passing a current through the MR sensor and measuring a voltage across the MR sensor. External circuitry then converts the voltage information into an appropriate format and manipulates that information as necessary to recover the data that was encoded on the disc.
The writer portion of the magnetic head for perpendicular recording typically consists of a main pole and a return pole which are magnetically separated from each other at an air bearing surface (ABS) of the writer by a nonmagnetic gap layer, and which are magnetically connected to each other at a region distal from the ABS by a back gap closure. Positioned at least partially between the main and return poles are one or more layers of conductive coils encapsulated by insulating layers. The ABS is the surface of the magnetic head immediately adjacent to the perpendicular medium. The writer portion and the reader portion are often arranged in a merged configuration in which a shared pole serves as both the top or bottom shield of the reader portion and the return pole of the writer portion.
To write data to the magnetic medium, an electrical current is caused to flow through the conductive coil, thereby inducing a magnetic field across the write gap between the main and return poles. By reversing the polarity of the current through the coil, the polarity of the data written to the magnetic media is also reversed. Data on double layer perpendicular media are recorded by a trailing edge of the main pole. Accordingly, it is the main pole that defines the track width of the written data. More specifically, the track width is defined by the width of the main pole at the ABS.
The main and return poles are made of a soft magnetic material. Both of them generate magnetic field in the media during recording when the write current is applied to the coil. However, the main pole produces much stronger write field than the return pole by having a much smaller sectional area the ABS and being made of magnetic material with higher magnetic moment. A magnetic moment of the main pole should be oriented along an easy axis parallel to the ABS when the main pole is in a quiescent state, namely without a write current field from the write coil. When the magnetic moment does not return to an orientation parallel to the ABS after being subjected to multiple instances of the write current field, the main pole is not stable. In an unstable pole, the orientation of the magnetic moment might remain nonparallel to the ABS position even after current to the write coil is turned off. Thus, the main pole may form a magnetic flux and may deteriorate or even erase data from the disc. Further, an unstable pole results in increased switching time when a current is applied. In a perpendicular head for ultra-high track density recording, the main pole is a predominant source of instability due to a strong demagnetizing field across the pole width at the ABS and the necessity of using magnetic materials with the highest possible values of magnetic moment saturation, even though these materials have poor anisotropy and relatively high coercivity.
A factor bearing upon the magnetic stability of the main pole and the return of its magnetic moment to an orientation parallel to the ABS is its uniaxial anisotropy. Uniaxial anisotropy is a measure of an amount of applied magnetic field required to rotate the magnetic moment of the main pole from the orientation parallel to the ABS to an orientation perpendicular to the ABS. If the uniaxial anisotropy is too low and the coercivity is high enough, the magnetic moment in the main pole may not always return to a position parallel to the ABS after a write current is removed. Thus, the erasure of recorded data on perpendicular media is likely.
Strength of the write field in the media is proportional to the magnetic moment of the main pole material. It is desirable to use a material with a high magnetic moment saturation (or high flux density saturation) for construction of the main pole in heads for ultra high track density recording. Accordingly, when the magnetic moment saturation of the main pole material is increased, a track width of the main pole tip can be reduced for increasing the storage capability of the disc drive. An example of a material with a high magnetic moment is an alloy of iron and cobalt (FeCo). The CoFe-alloy will conduct a large amount of flux and thereby permit the use of a very narrow pole tip, resulting in a very narrow track width, thereby allowing for ultra-high recording densities. Unfortunately, while CoFe films have the highest magnetic moment saturation, they do not have good magnetic stability due to poor anisotropy and relatively high coercivity. This means that the magnetic moment might not return to the parallel position to the ABS after being subjected to multiple instances of the write current field in the main pole tip of submicron width.
Accordingly, there is a strong-felt need to provide a writer which is magnetically stable and is made of material with high magnetic moment saturation. Such a stable writer will reduce switching time, increase a drive""s data rate, and prevent unintentional erasing on perpendicular media after the write current is turned off.
The present invention is a perpendicular writer having an air-bearing surface, a main pole with a main pole extension, and return pole, and a back gap closure intermediate the main pole extension and the return pole. The main pole extension is in direct contact with the main pole and recessed from the air-bearing surface to prevent erasure of recorded data on adjacent tracks. The main pole includes a top magnetic layer, a soft magnetic underlayer and a nonmagnetic spacer placed in-between. The top magnetic layer forms a trailing edge of the main pole at the ABS and has a magnetic moment greater than that of the soft magnetic underlayer. The soft magnetic underlayer is in direct contact with the main pole extension made of magnetic material with low coercivity, high anisotropy, and high permeability. Further, the top magnetic layer and soft magnetic underlayer are antiferromagnetically coupled through the thin nonmagnetic spacer. The nonmagnetic spacer has predominantly 111-crystalline texture and promotes reduction of coercivity and grain size along with an increase of anisotropy of the top magnetic layer material.